Natural killer cells provide protection from numerous viruses in the early stages of the infection. NK cell[unreadable] activity is controlled by cytokines and cell surface stimulatory and inhibitory receptors. The NKG2D[unreadable] stimulatory receptor has been implicated in the recognition of cells infected with viruses. NKG2D recognizes[unreadable] the RAET1 (including several subfamilies) and MIC families of cell surface ligands, which are poorly[unreadable] expressed on the surface of most normal cells. MIC and RAET1 family members are transcriptionally[unreadable] upregulated in cells infected with herpesviruses and most likely other viruses. Our expertise on immune[unreadable] recognition by NK cells (Raulet) and viral immune evasion strategies (Coscoy) will be combined to[unreadable] investigate our hypothesis that viral infection leads to generic signals that upregulate transcription of NKG2D[unreadable] ligands, but that some viruses evade recognition by preventing ligand expression at the cell surface. The[unreadable] long term aim of these studies is to provide routes to develop therapeutic agents that enhance NK cell[unreadable] responses to viruses, especially in the context of biodefense. Our aims are to 1) focus on two herpesviruses[unreadable] to elucidate mechanisms that upregulate expression of NKG2D ligands in virus-infected cells, including the[unreadable] role of Toll like receptors, cytokines, interferons and the DNA damage pathway; 2) Examine representatives[unreadable] of 8 virus families, including several relevant to biofense, for their capacity to upregulate NKG2D ligand[unreadable] mRNAs and downregulate ligand proteins; by examining a panel of mutant fibroblasts defective in a broad[unreadable] array of protective functions, we expect to learn the factors responsible for ligand upregulation in different[unreadable] viral systems; 3) Determine how MHV68, a mouse gamma herpesvirus, evades NKG2D ligand upregulation,[unreadable] and, using two-photon microscopy, determine how NKG2D-ligand interactions impact NK cell-target cell[unreadable] interactions in vivo; 4) Determine whether the pathways uncovered in the mouse system in aims 1-3 regulate[unreadable] human NKG2D ligands in human cells infected with two herpesviruses, HCMV and KSHV. Importantly,[unreadable] aspects of this project will be part of a collaborative effort between the different groups participating in this[unreadable] PO1 application.